FACIES AND ROCK TYPE ANALYSIS OF BATURAJA FORMATION, NARA FIELD, NORTH WEST JAVA BASIN

• Main Author: Yulanda Septianty, Nurul
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/64000
• Institution: Institut Teknologi Bandung

The increasing demand of energy pushes oil and gas companies to develop their existing wells due to effectiveness and economy factor. Nara Field is a part of North West Java Basin which is in development stage. The reservoir of the field is from Baturaja Formation which consists of carbonate rocks that has no linear relation between its porosity and permeability, unlike silisiclastic rocks. Therefore, facies, facies association, and rock type are important to be conducted to determine the relation to find reservoir with best quality which is economically prospective. This is what leads the researcher to analyze facies and facies association, rock type, and rock type prediction for Baturaja Formation in Nara Field. This research focuses on carbonate rocks of Baturaja Formation and the objective is to determine the facies, facies association, rock type, rock type prediction, and determination of relation between facies, facies association, and rock type. The research is conducted by analyzing core plugs of three wells, thin sections of two wells, well log data of 19 wells, and is also supported by Routine Core Analysis (RCAL) data of four wells. There are five steps of analysis which are facies analysis, facies association analysis, rock type analysis, rock type prediction, and reservoir quality determination. The result of facies analysis shows that the focused area is consisted of 10 facies which are Skeletal Grainstone, Skeletal Packstone, Miliolid Packstone, Large Benthic Foraminiferal Packstone, Large Benthic Foraminiferal Grainstone, Coral Boundstone, Coral Floatstone, Coral Grainstone, Foraminiferal Packstone, and Foraminiferal Wackestone which assemble the Platform Interior and Platform Margin Reef facies association. Then the result of rock type analysis by using Flow Zone Index (FZI) method shows that there are 10 rock types in which each has types of porosity. Rock type DRT=6 is a reservoir with the worst quality caused by its lowest FZI value of 0,12 – 0,11 micron and has vuggy, intraparticle, and intercrystalline porosity. Rock type DRT=7 with FZI value of 0,20 – 0,16 micron has vuggy, fracture, and intraparticle porosity. Rock type DRT=8 with FZI value of 0,34 – 0,22 micron has vuggy, intercrystalline, and fracture porosity. Rock type DRT=9 with FZI value of 0,57 – 0,36 micron has vuggy, intercrystalline, and intraparticle porosity. Rock type DRT=10 with FZI value of 0,94 – 0,59 micron has vuggy, intercrystalline, and intraparticle porosity. Rock type DRT=11 with FZI value of 1,55 – 0,96 micron has vuggy, intercrystalline, and micropore porosity. Rock type DRT=12 with FZI value of 2,34 – 1,66 micron has vuggy, intercrystalline, and micropore porosity. Rock type DRT=13 with FZI value of 3,09 – 2,67 micron has vuggy, intraparticle, and interparticle porosity. Rock type DRT=14 with FZI value of 6,95 – 4,43 micron has vuggy, intraparticle, and interparticle porosity. Rock type DRT=15 is a reservoir with the best quality indicated by its high FZI value of 8,25 – 7,09 micron and has vuggy, fracture, and micropore porosity. The difference is caused by diagenetic processes occurred in Nara Field, which are micritization, dissolution, cementation, neomorphism, and compaction. These processes happened in meteoric vadose, meteoric phreatic, marine phreatic, and burial diagenetic environment. After that, the result of rock type prediction by using Multi – Resolution Graph-Based Clustering (MRGC) indicates that by comparing three parameters which are gamma ray log, density log, and neutron log, the 22 electrofacies cluster model has the most suitable prediction to represent 10 rock types from RCAL data. Furthermore, the equivalence between facies, facies association, and rock type is used as the lead to determine reservoir quality. The reservoir quality of Platform Interior is better than the reservoir quality of Platform Margin Reef. This is caused by the different rock type and porosity type dominating each facies association. Platform Interior is mostly consisted of rock type DRT=14 with percentage of 31%, whereas Platform Margin Reef is dominantly composed of rock type DRT=10 with percentage of 42%. Other than that, Platform Interior has significant composition of fracture porosity with percentage of 13% that indicates better flow character. Fracture can be found on Large Benthic Foraminiferal Packstone, Miliolid Packstone, and Skeletal Packstone facies. The result of this research hopefully can be considered in searching for the next prospective zones to develop.